SCP-XXXX is to be kept within A 10x10m containment cell equipped with a full bathroom set; a bookshelf stocked with new books everytime subject requests; a twin sized bed; a clothing dresser; a small table and chair.
10x10m is two dimensions. What's the third? "every time," not everytime. Couldn't you just put it in a standard humanoid containment cell? Why does it get the privilege to request books whenever it wants?

SCP-XXXX is to be fed 3 times a day and is to be let out in the courtyard to exercise whenever subject asks.

You don't have to include meals. You can assume it's being fed. Unless it requires a specific meal. Why does it get the privelege to go to the courtyard whenever it wants? Also, where even is it being contained?

SCP-XXXX is to be spoken too with a calm and peaceful tone and one guard is to be guarding his containment cell from the times of 7 am to 9 pm and is not to let out of his cell after the time of 8:00 PM. The lighting is SCP-XXXX's containment chamber are to be halogen. there can not be any neon light within SCP-XXXX’s imediate vacinity.

Change it to "to," not too. "Peaceful" town doesn't sound very clinical. And why does it need to be spoken to in this tone? The first sentence is also a run on sentence. "Its," not "his," the SCP is an object and not a person. Why does it specifically have to be guarded from 7 AM to 9 PM? What about 10PM through 6:59 AM? Change "and is not to let out of his cell after the time of 8:00 PM" to "and is not to be let out of its cell after the time of 8:00 PM." Why specifically after 8:00? "are to be" should be "are to be made up of". Capitalize "There" in the last sentence; "immediate," not "imediate." Put "vicinity," instead of "vacinity." Also, what is defined as its "immediate vicinity?" Just for the sake of clarification.

Description:

Bold it.

SCP-XXXX has the ability to use projectile neon shards, the range of said shards is approximated to be 65 meters. when in the immediate vicinity of a strong neon light source SCP-XXXX possess the ability to fire six of these shards in a pattern similar to twelve-gauge buckshot.

How do these shards look? Capitalize "when." Put a comma after "light source." I personally don't know what a twelve-guage buckshot is. Maybe you could describe it and then use that as an example.

SCP-XXXX also poses the ability to conjure a blade similar in composition to the shards, this blade measures approximately 110 centimeters in length and does not differ in function form a normal steel blade, although it is much sharper. the edge of the blade measures approximately one neon atom in width ( 1 × 10 to the -12 power meter).

"conjure" doesn't seem very scientific. Maybe "create," or "produce?" The first sentence feels like it's too long. It's "from" not "form." The edge is one neon atom in width? How does anyone see that?

SCP-XXXX can also self-heal and heal others with this power, however if killed SCP-XXXX is unable to heal this hypothetical person(s). SCP-XXXX is also able to perform a “flash step” moving from one point to another in a blink of an eye, SCP-XXXX is unable to perform this ability in rapid succession as it “drains” SCP-XXXX’s “powers” very quickly. SCP-XXXX also holds the ability to use neon to sprint faster, reaching speeds of nearly 100 km/h.

How can it self heal using neon? How does the foundation know that "Simon" can't heal a dead person if it hasn't been tested; "blink of an eye" doesn't seem scientific. Why is it able to teleport? Why is the teleportation called a "flash step?" Why does neon let this SCP sprint faster? Why does using its teleportation drain its "powers?"

Dr.Prescott: Okay Simon, please aim directly at the target and use your buckshot. "Simon" is an object, not a person.
Simon: Are we done for the day Dr.Prescott.

"Are we done for the day, Dr. Prescott?"

Dr.Prescott: Simon if he didn’t do anything wrong he wouldn’t be here, now do as you’re told.

I don’t know why, but I feel like Simon is more than a number, he’s a person going through real problems, problems that a good portion of the world has too. I think he could be useful to the foundation, not as a “Subject” or an SCP, but as a person. I’ve had really good conversations with Simon, he shows great intelligence especially in writing and literature, and he shows compassion to those who suffer with depression or those who are just having an off day, I get comments like this from the guards at his cell. I hate how the foundation sees him, when everyone who’s come into contact with him genuinely feel he’s just another person. I am formally requesting that Simon is to be treated like foundation staff and become a member of site-██’s medical team and have a personal quarters, and also that he gets a real therapist instead of the hog you hired. His potential for the medical team here is immeasurable and he’s a real pleasure to have around.

Signed -Dr.Prescott

Dr. Prescott writing to the council seems a bit far fetched to me. "Instead of the hog you hired," isn't something a Foundation member would say when writing to the highest authority in the foundation.